Discrete volumes of a first fluid separated from one another by a second fluid that is immiscible with the first fluid, can sometimes undesirably coalesce with one another. Efforts to prevent such coalescence of discrete volumes can render the addition of a miscible fluid to the discrete volumes unfeasible. It would be desirable to prevent coalescence between two such adjacent immiscible fluid discrete volumes yet permit the addition of a third or addition fluid into one or both of the adjacent discrete volumes.